The word ego appears several times in Freud's "The Uncanny." He uses the word when describing his concept of the 'double' in relation to the uncanny (142-3). According to Merriam-Webster Online, the ego is "one of the three divisions of the psyche in psychoanalytic theory that serves as the organized conscious mediator between the person and reality especially by functioning both in the perception of and adaptation to reality." To best understand Freud's concept of the ego, compare this definition to super-ego and id. Also, Wikipedia has an informative entry under "Id, ego, and super-ego."